Double Resonance SERS Substrates: Ag Nanoparticles on Grating

Silver nanoparticles grown in nanochannels of anodic aluminum oxide on a grating form a surface-enhanced Raman scattering (SERS) substrate with the double resonance from both localized and delocalized plasmons. With angle-resolved reflectance spectroscopy, we characterized the propensity of surface plasmon polariton (SPP) of the grating and confirmed it with electrodynamic simulation. In addition to the hot spots created between adjacent silver nanoparticles, the extra SERS enhancement engendered by the grating's SPP manifested as the enhancement band over a range of detection angles. The SERS signal of thiophenol obtained with transverse-magnetic excitation showed a gain by a factor of 2, which is comparable with the one estimated from local-field simulation. The electrodynamic simulation showed that the most normally directed local field at the surface may limit the field enhancement of localized plasmonic coupling between silver nanoparticles. With the incorporation of grating, the enhanced SERS signals are inherently wavelength-dispersed, thus enabling simpler designs of SERS-based sensors without a spectrometer.